This invention relates to self-cleaning ovens using a pyrolytic process at a high temperature range above normal cooking temperatures, between about 750.degree. F. and about 950.degree. F. of the type fully disclosed in U.S. Pat. No. 3,121,158 assigned to General Electric Company, the assignee of the present invention. In such high temperature oven-cleaning operations, it is best to maintain the oven wall temperature at substantially uniform temperatures throughout so as to avoid hot spots which may damage the oven liner, and also cold spots which would cause soil or food by-product deposits to remain or not be fully decomposed. With regard to cold spots, it should be noted that heat tends to be dissipated through and around the oven door at a higher rate than at other areas of the oven. One of the causes of heat dissipation is that in some heat cleaning oven designs air for decomposition of food by-products, as well as conventional baking, is allowed to enter the oven cavity through the door seal area and, more particularly, between the lower edge portion of the door and oven cavity. It has been common practice in self-cleaning ovens of the type disclosed in U.S. Pat. No. 3,121,158 to incorporate a mullion heater to supply additional heat adjacent the front of the oven liner to replenish this heat loss. While the additional heat source has been effective in preventing cold spots and insuring uniform cleaning of the oven walls, the employment of the additional heater adds considerably to the cost of the ovens. This is reflected not only in the cost of the additional heating element employed but also in the higher cost of fabricating the additional members and assembling them. Other methods of preventing heat loss or cooling of the oven liner adjacent the oven opening are typically disclosed in U.S. Pat. Nos. 3,066,212 and 3,038,426 wherein the oven liner is thermally isolated from the surrounding cabinet.